An appeals court on Thursday upheld a lower court's ruling that a progressive teachers' union is not a legitimate labor group because its members include fired teachers.

In October 2013, the Korean Teachers and Education Workers Union filed a lawsuit with the Seoul Administrative Court against a government's decision to outlaw the KTU due to the union's repeated refusal to deny membership to nine fired teachers.

Under the law, dismissed teachers are not eligible to join a trade union.

The Seoul High Court said the government's decision was legitimate based on the law.

The ruling, if upheld by the Supreme Court, would ban the KTU from using the title "labor union" and engaging in legitimate negotiations with school authorities. The union's full-time staff members should also return to teaching jobs at schools.

Founded in 1998, the progressive teachers' union became a legitimate organization the following year under the liberal government led by President Kim Dae-jung. (Yonhap)